[Eddie B]

I have a 2005 Nissan Titan and want to get a handle on a heater issue before it gets 20 below. When it is above 0 the heater blows hot air and will get very warm inside. Last year when it got 20 below it only would blow luke warm air and would not heat the inside of the cab very well. The temp. gauge would register normal, and the antifreeze was full. Am I looking at replacing the thermostat, or something else? Thanks in advance